1. Field
This invention relates generally to semiconductor chip devices, and in particular to the manufacture of a heat spreader lid that is part of a multi-piece integrated heat spreader/heat sink/stiffener assembly in a semiconductor package which reduces stress and warping of a semiconductor die during attachment of the die to a substrate.
2. Description of the Prior Art
In semiconductor device assembly, a semiconductor chip (also referred to as an integrated circuit chip or “die”) is bonded directly to a packaging substrate. Semiconductor packages that have been soldered to a motherboard and placed in a computer are typically subjected to temperature cycling during computer operation. Therefore, the semiconductor packages require a way to permit excess heat to be radiated into the surrounding air so that the heated air can be removed by cooling fans. A heat spreader lid, composed of a high thermal conductivity material, and having substantially the same dimensions as the package substrate, is attached over the die and bonded by a thermally conductive adhesive which is heat cured. A conventional heat spreader is typically a flat piece of nickel-plated copper about 20 to 40 mils thick. A metal plate called a heat sink, which includes metal fins to promote rapid radiation of excessive heat, is bonded by a thermally conductive adhesive to the flat surface of the heat spreader lid. The purpose of the heat spreader and heat sink is to disperse the heat generated during thermal cycling in order to reduce stress in the package due to different coefficients of thermal expansion of the various elements of the package, including the die, substrate and underfill. Such stress in the semiconductor package may ultimately result in electronic and/or mechanical failure, including cracking of the die. It is desirable that the lid be in the form of a cap with side that will fit over the semiconductor package to further constrain the substrate in order to prevent warping or other movement relative to the die which may be caused by thermal cycling.
Conventional processes for manufacturing a heat spreader use a progressive die wherein raw material is taken from a copper coil and run through a progressive die (blanking, coining and piercing) so that the result at the end of the progression is supposed to be a finished part. The problem with this process is that it does not result in a part off of the coining press that meets minimum specifications for flatness. There must be subsequent grinding and finishing to bring the part into compliance with minimum specifications for flatness, which is critical for the heat spreader to make uniform contact with the semiconductor die.